Measurement of the neutrino oscillation parameters using Bayesian Markov Chain Monte Carlo at T2K

中微子是宇宙中最丰富的物质粒子，但人们对它们知之甚少，因为它们相互作用很弱。很长一段时间以来，人们一直认为中微子是无质量的，但在大约20年的时间里，越来越多的证据表明，不同类型的中微子可以从一种口味转变为另一种口味。这一发现被称为中微子振荡过程，因为它们在不同的味道之间来回移动，被授予2015年诺贝尔物理学奖，分别授予Takaaki Kajita和Arthur B.McDonald分别使用SuperKamiokande和SNO实验。虽然这些实验使用的是天然的、不太了解的中微子来源，但T2K实验更进一步。位于日本东海岸的J-PARC加速器中心在受控环境中产生了I束Muon中微子，并将其定向到SuperKamiokande探测器。该光束被测量了两次，一次是在中微子可能发生变化之前在距离中微子产生目标280米的附近的探测器中测量，另一次是在下游300公里处使用SuperKamiokande探测器测量。通过比较两个探测器的测量结果，可以精确确定振荡参数。此外，T2K已经对中微子和反中微子进行了这些测量，这导致了一些初步的迹象，表明振荡不同，因此违反了CP对称性。这意味着物质和反物质的行为并不相同，最终可能有助于解释宇宙中物质和反物质的不对称性，这完全是由物质主导的。这篇论文将作为国际T2K合作的一部分进行，该合作拥有来自全球的约500名成员。这篇论文的目的是通过获取更多的数据来改进控制中微子振荡的参数的测量，以减少统计不确定性，同样重要的是，减少测量的系统不确定性。学生将使用T2K振荡分析团队之一，开发更好地处理或减少系统误差的新方法，并将这些应用于现有的和新的数据集。这些方法将需要仔细验证，并将结果与替代分析团队的结果进行比较。马尔可夫链蒙特卡罗方法很可能被用来在高维参数空间中寻找最优解。这还没有使用近探测器数据来完成，这将允许对相关和不相关的不确定性进行更一致的处理，并同时对近探测器和远探测器数据进行拟合，从而提高对CP违反效应的敏感性。

Neutrinos are the most abundant matter particle in the Universe, but very little is known about them as they only interact weakly. For a long time it had been assumed that neutrinos would be massless, but since roughly 20 years, there has been mounting evidence that the different kind of neutrinos can transform themselves from one flavour to another. The discovery of this is process called neutrino oscillations as they go forth and back between the different flavours was awarded with the Nobel Prize in Physics in 2015, which was awarded to Takaaki Kajita and Arthur B. McDonald using the SuperKamiokande and SNO experiments respectively.While these experiments were using natural not very well understood neutrino sources, T2K experiment has gone a step further. I beam of muon neutrinos is produced in a controlled environment at the J-PARC accelerator centre on the east coast of Japan and is directed to the SuperKamiokande detector. The beam is measured twice, once in a near detector 280m away from the neutrino production target before the neutrinos could change and once with the SuperKamiokande detector 300 km downstream. Comparing the measurements of both detectors allows a precision determination of the oscillation parameters. Furthermore, T2K has made these measurements with both neutrinos and anti-neutrinos and this lead to some first indications that the oscillations are not the same and thus violate the CP-Symmetry. This means that matter and anti-matter do not behave the same and may eventually help to explain the matter anti-matter asymmetry of the universe, which is entirely matter dominated.The thesis will be performed as part of the international T2K collaboration, which has around 500 members from around the globe. The aim of the thesis is to improve the measurement of the parameters governing neutrino oscillations by taking additional data to reduce the statistical uncertainty and, equally important, to reduce the systematic uncertainties of the measurement.The student will use one of the T2K Oscillation analysis teams and develop new methods that better treat the systematic errors or reduces them and apply these to existing and new data sets. The methods will need to be carefully verified and the results compared to those of alternative analysis teams. It is likely that a Markov Chain Monte Carlo approach will be used to find optima in a highly dimensional parameter space. This has not yet been done using the near detector data and would allow for a more consistent treatment of correlated and uncorrelated uncertainties and a simultaneous fit to the near and far detector data leading to an improved sensitivity to CP-violating effects.